The present invention relates to a clean room device, and more particularly, relates to a clean room device of a semiconductor manufacturing plant or the like where a high cleanliness is necessary.
At a ceiling of a room of a clean room device of a semiconductor manufacturing plant or the like, ceiling frames are arranged like a grid, and to each grid space formed by these ceiling frames, a fan filter unit is provided. The fan filter unit sends the air in the space over the ceiling (hereafter, referred to as the over-ceiling space) of the room into the room while removing the dust with the filter, by driving the fan. The sent-in clean air flows downward, and flows to the space under the floor (hereafter, referred to as the under floor space) through the grating floor at the under surface of the room together with the dust in the room, and part of that is introduced into the over-ceiling space through the circulating passage, and the residual air is exhausted to the outside of the clean room device. The air introduced into the over-ceiling space is sent in the room while the dust is removed again with the above-described fan filter unit. The air in the room is thus kept clean.
The fan filter units are not always provided to all grating spaces, but in some cases, they are arranged at certain distances for the reduction of the installation cost or the running cost. In those cases, at each grid space where no fan filter unit is provided (hereafter, referred to as the open grid space), a closing plate which completely shuts off the over-ceiling space and the interior of the room has conventionally been provided for preventing the air before the purification in the over-ceiling space from flowing into the room.
However, if the fan filter units are arranged at distances and the closing plate is provided at the open grid space conventionally, there has been such a weak point that the cleanliness in the room can not be raised when compared with the case where the fan filter units are provided at all grid spaces.
The present invention is achieved due to such a situation, and it is an object to provide a clean room device in which the cleanliness in the room can be raised even if the fan filter units are arranged at large distances.
Conventionally, generally it has been considered that the cleanliness in the room of the clean room device depends on the air volume of the clean air sent into the room, that is, it is necessary to increase the air volume of the clean air for improving the cleanliness in the room. Accordingly, it has been considered that the reason why the cleanliness in the room cannot be raised if the fan filter units are arranged at large distances depends on the reduction of the air volume of the clean air.
However, by following the reason why the cleanliness in the room falls when the fan filter units are arranged at distances, it has become clear that the reason is not the reduction of the air volume of the clean air, but the occurrence of the swirling current at the area under the closing plate provided at the open grid space where no fan filter unit is provided, which causes the dust to stay in the room at that area.
The present invention is achieved by giving attention to this point, and it attains the improvement of the cleanliness in the room where the fan filter units are arranged at distances, by preventing the occurrence of the swirling current in the room.
In order to attain the above-described object, the clean room device of the present invention includes: a room with a ceiling; a fan filter unit which is provided at the above-described ceiling to send clean air into the above-described room from the over-ceiling space; and a breathable body which is provided at the above-described ceiling, characterized in that part of the air in the above-described room flows into the above-described over-ceiling space through the above-described breathable body, by the difference between the air pressure in the above-described room and the air pressure in the above-described over-ceiling space.
According to the present invention, in the ceiling of the room, at the open grid space where no fan filter unit is provided, a breathable body is provided, and by the difference between the air pressure in the room and the air pressure in the over-ceiling space, part of the air in the room is made to flow into the over-ceiling space through the breathable body. Consequently, it is possible to prevent the occurrence of the swirling current at the area under the open grid space, and the cleanliness in the room can be raised.
It is also possible to use a filter for the dust collection as the breathable body. Consequently, it is possible to collect the dust in the air passing through the breathable body by the filter, so that the load of the filter in the fan filter unit is reduced, and in the meantime, it is possible to prevent the dust in the over-ceiling space from entering the room.
Furthermore, it is also possible to provide the fan over the breathable body with a filter. By operating the fan and sending the air from the over-ceiling space through the filter of the breathable body into the room, it is possible to make the filter of the breathable body perform the action of the filter of the fan filter unit, and therefore, it is especially advantageous in the case where a high cleanliness is required at the area under the open grid space. Furthermore, by reversely operating the fan and sucking part of the air in the room through the filter of the breathable body into the over-ceiling space, the air volume of the air flowing to the over-ceiling space from the room can easily be controlled. Furthermore, in the case where the air pressure in the room is higher than the air pressure in the over-ceiling space, part of the air in the room can be made to flow to the over-ceiling space, even if the fan is stopped.
It is also possible to use a perforated plate as the breathable body. By preparing a plurality of perforated plates with different opening ratios, that is, with different breathabilities and properly selecting a suitable plate among them to be provided, or by using a perforated plate whose opening ratio is adjustable, the air volume of the air flowing from the interior of the room through the breathable body into the over-ceiling space can easily be controlled.
Furthermore, the breathable body may be constructed by a filter and a perforated plate. Consequently, the dust in the air passing through the breathable body is collected by the filter, so that the load of the filter in the fan filter unit is reduced, and in the meantime, it is possible to prevent the dust in the over-ceiling space from entering the room. Moreover, by controlling the breathability of the breathable body by using the perforated plate, it is possible to easily control the air volume of the air flowing from the room through the breathable body into the over-ceiling space.
The breathable body preferably has such a breathability that when the air pressure in the room is higher than the air pressure in the over-ceiling space by 0.2 mmAq to 1.5 mmAq, the total air volume of the air flowing into the over-ceiling space through the breathable body from the room becomes 5% to 15% of the total air volume of the air to be sent into the room from the over-ceiling space by the fan filter unit. Consequently, it is possible to effectively prevent the occurrence of the swirling current in the room while keeping the cleanliness in the room.